Si对Mg-7Al-2.5Ca-0.4Mn-0.25Sr合金铸态组织的影响

Effect of Si Addition on As-Cast Microstructure of Mg-7Al-2.5Ca-0.4Mn-0.25Sr Alloy

通过光学显微镜、扫描电镜和X射线衍射分析等,研究了Si对铸态Mg-7Al-2.5Ca-0.4Mn-0.25Sr合金显微组织的影响。结果表明:Mg-7Al-2.5Ca-0.4Mn-0.25Sr-xSi(x=1,2,3)合金主要由α-Mg基体、AlMn相、Mg2Ca相、Al2Ca相和CaMgSi相组成。CaMgSi相含量随Si元素的增加而增加。Si含量由1%提高到3%会引起三方面变化:一是使α-Mg枝晶变得发达;二是析出的共晶组织(Mg2Ca+Al2Ca)含量有所减少;三是促进CaMgSi相的析出,且CaMgSi相的形貌逐渐由空心块状向针状、再向汉字状演化,因此合金中Si的合适加入量应控制在2%左右。对组织的演变过程进行了讨论。

The effects of Si on the as-cast microstructure of Mg-7Al-2.5Ca-0.4Mn-0.25Sr alloy were investigated by using the optical microscopy, scanning electron microscope and X-ray diffraction. The results indicate that the as-cast microstructure of Mg-7Al-2.5Ca-0.4Mn-0.25Sr-xSi （x=1, 2, 3） alloys are mainly composed of α-Mg matrix, AlMn, Mg2Ca, Al2Ca and CaMgSi phases, the volume fractions of CaMgSi phase increases with increasing the Si element. The addition of Si ranging from 1% to 3% results in α-Mg dendrites developing, the eutectic （Mg2Ca＋Al2Ca） decreasing and CaMgSi phase increasing, and the morphology of the CaMgSi phase gradually changes from hollow block to needle, then evolves into Chinese script, which was discussed in the paper.